textproduct: Rapid City

KEY MESSAGES

- Marginal to Slight (Level 1-2 out of 5) risk of severe thunderstorms this evening.

- Isolated strong/severe thunderstorms possible Monday afternoon/evening.

- Upper ridge will dominate the weather with subtle disturbances through next week with temperatures about 4-8F above normal

DISCUSSION

(This Afternoon Through Saturday) Issued at 1043 AM MDT Sun Aug 23 2026

16z surface analysis had frontal boundary from eastern MT to eastern CO and a trough from eastern CO into northeastern NE. Water vapour loop had upper ridge over the southwest CONUS with a shortwave over north-central WY. Overnight MCS about to fully exit the CWA with leftover low stratus burning off per 0.5km 1-minute visible imagery. Main concern this forecast will be effect of north-central WY shortwave.

This afternoon/tonight, shortwave moves into the Dakotas with slight increase in mid-level flow resulting in 30-45kt effective bulk shear later this afternoon. Td/s in the 60s will be sustained per breezy southeast winds ahead of frontal boundary. Band of 2-3KJ/kg MLCAPE forecast this afternoon over far western SD with minimum cap. Convective initiation (CI) will likely be over the Black Hills around 20z with supercells moving south/southeast at 10-20kts per Bunkers storm motion prognostications. Another area of strong/severe CI may develop over northwestern SD along the frontal boundary/trough interaction late this afternoon. CAMs handle this scenario in different fashion with some emphasizing MLCIN east of the Black Hills with some members not so much. Other strong/isolated severe convection may occur over the rest of the CWA. Sufficient buoyancy/bulk shear for marginal/slight (1-2 out of 5) of severe thunderstorms. Large hail/damaging wind the main threats with CIG1 magnitudes over western SD. Temperatures will be a bit below guidance this afternoon per low level moisture/dissipating stratus.

Monday, diurnally driven convection possible in the afternoon/evening, but the upper support less certain compared to today. Temperatures will be near guidance.

The rest of the forecast will be dominated by the upper ridge over the southwest CONUS. Ridge amplification into the northern Plains for the second half of the week suggests somewhat quieter and drier weather.

AVIATION

(For the 00Z TAFS Through 00Z Monday Evening) Issued At 545 PM MDT Sun Aug 23 2026

Isolated thunderstorms this evening will continue to produce hail, gusty winds, and brief vsby drops to MVFR for a few more hours, especially across the northwestern South Dakota plains, with VFR conditions otherwise dominating. PROB30s have ended at the TAF terminals. Additional isolated thunderstorms are possible Monday afternoon and evening, with CAMs currently offering the best consensus over the Black Hills (initiation around 19z/1pm) spreading ESE across the I-90 corridor and southern South Dakota plains through evening. A new PROB30 has been added for KRAP.

UNR WATCHES/WARNINGS/ADVISORIES

SD...None. WY...None.